The invention concerns a method of making a fabric having a finish produced on at least one side by means of a coherent surface layer.
It is known to finish the surfaces of support materials, such as textile support materials, for example, and also the surfaces of wood, plastic, metal or the like, by means of surface coatings. These surface coatings are, as a rule, of an impermeable, film-like nature, and bring about an improvement of the mechanical properties of the base materials as regards wear-resistance, surface roughness, tear strength, or the like, and at the same time they protect against attack by liquids and gases which may have a harmful effect on the base material.
At the same time, the surface coatings block the emergence of volatile components of the base material or their penetration through the base material, and, lastly, they bring about a visually appealing sheen.
Numerous processes are known for the production of the surface coatings outlined above. For example, the surface coatings can be produced by direct or reversal processes, by mechanical spraying, casting, roller application, pressing or dipping. Liquid systems, particularly plastisols, dispersions or dissolved plastics are applied, which are then hardened in some suitable manner by a physical or chemical process. The applicability of all these processes is limited by the interaction of the coating systems with the base material. To obviate this disadvantage, it has also been proposed to bond systems which have fully reacted and contain no solvents, such as films for example, onto support materials. This bonding process also results in a film-like surface, which is mostly impermeable. The process, however, is limited by the often less than optimum adherence between the materials to be bonded together. The bonding of impermeable films onto impermeable support materials with the aid of adhesives containing solvents is particularly problematical.
The object of the invention is the development of a process for the production of materials finished at least on one side by means of a coherent surface layer, which will make it possible to adapt the properties of the surface finish with regard to porosity or microporosity or permeability to vapors and gases to a particular application without great effort in experimentation, particularly when microporous surface layers and layers permeable to vapor and gases are desired, but also when completely impermeable layers are desired.
A process is proposed which is characterized in that a very fine fiber mat of staple and/or endless fibers is applied to the side or sides of the support material which are to be finished, and the mat thus deposited is then consolidated and smoothed, with the application of pressure if desired, whereupon it simultaneously enters into a firm bond with the surface of the support material that is thus finished.
The process is particularly conceived for very fine thermoplastic fibers which are consolidated without the use of an additional binding agent by the application of pressure and heat in a known manner, and are simultaneously smoothed to form the coherent surface layer, it being possible to vary and quite precisely control the properties of this surface layer as regards porosity or microporosity and permeability to vapors and gases by the application of the optimum pressures and temperatures for the desired purpose. The term "very fine fibers," as used herein, is to be understood to mean fibers of a diameter of about 0.1 to 30 microns, fiber diameters of about 1 to 20 microns having proven to be particularly suitable.
The very fine fibers can be produced in any desired manner, i.e., very fine fibers prepared in any desired manner can be applied to the surfaces of the support materials that are to be finished, and the surfaces can then be finished in the manner described by the invention, by consolidation and smoothing of the fiber covering while simultaneously bonding it to the support material.
The very fine fibers may comprise nylon, polyester, polyethylene, polypropylene, polystyrene, acetate, polycarbonate, polysulfone, and the like, being as short as some millimeters up to centimeters as well as endless. They may be deposited from about 5 to 50 g/m.sup.2 onto substrates which can be of varied composition, e.g. woven or non-woven textiles, artificial leather of polyurethane or other base, foams of polyurethane or rubber, plastic foils, or even wood or aluminum.
Surprisingly, however, it has been found that very fine fibers which are obtained by means of an electrodynamic spray process and are sprayed directly onto the support material, produce, after consolidation and smoothing in accordance with the invention, a surface finish which is not only especially attractive in appearance, but also one which can be controlled with regard to its characteristics of porosity and permeability in a manner which hitherto has never been achieved. Thus it is possible, for example, by the use of very fine thermoplastic fibers and thermal consolidation and smoothing, to provide a top layer on a textile support material and thereby obtain a laminate having properties virtually equal to those of natural leather. From the process point of view, this leather substitute material is extraordinarily simple to produce. All that is necessary is to apply to a woven or nonwoven textile fabric very fine fibers obtained and sprayed on by electrostatic methods and then, in a single calendering process, to smooth and consolidate the very fine fiber mat thus deposited.
In the performance of the electrostatic spray process, apparatus which have proven to be especially effective are those which are described in U.S. Pat. No. 4,069,026 and in commonly assigned patent Application Ser. No. 792,260, filed May 2, 1977, now U.S. Pat. No. 4,144,553, the disclosure of which is incorporated herein by reference.
If the material to be surface finished is sprayed by means of a suitable spray electrode, such as the kind described in the two patent applications mentioned above, a very uniform, very fine fiber mat free of solvent and binding agent, formed of fibers of a diameter of about 0.1 to 30 microns, will be deposited thereon. Then the fiber mat sprayed on the surface is consolidated as desired, by heat and pressure, in the described manner. Transparent or opaque surfaces can thus be obtained, which will satisfy requirements of fashion materials with regard to appearance. Without the otherwise necessary expense, either high-gloss or matt surfaces can be produced. The surface layers will be microporous or impermeable, according to their method of manufacture.
Suitable spray media are known lacquer systems, dissolved plastics, dispersions, or mixtures of solids. Particularly broad in its usefulness in this connection is the apparatus described in U.S. Pat. No. 4,144,553 for electrodynamic spraying, which also permits the patterened application of very fine fiber mats to the support material by means of the masking described therein.